Field of the Invention
This invention relates to lifts for elevating objects and, more particularly, to a lift for a marine craft.
Background Art
It is desirable to store marine craft out of water for various reasons and particularly because such storage may lengthen the life of the hull. Deterioration of the hull due to marine life accumulation is obviated Further, the raised hull will not be subjected to rough water which might throw the craft against its mooring or cause it to overturn.
Designers of boat lifts strive towards simplicity, compactness, and ease of operation, which objectives are often competing.
One type of prior art boat lift is shown in U.S. Pat. No. 4,318,632, to Fortmeyer. In Fortmeyer, a boat support platform is connected to a frame for pivoting movement relative to the frame between lowered and raised positions. A lifting force is imparted through a cable, which is retrievable by a winch. In Fortmeyer, there is a concentration of the lifting force on only one side of the platform. If the weight of the boat is substantial this lifting force tends to skew the structure, with obvious detrimental results.
An alternative type of prior art lift is shown in U.S. Pat. No. 4,022,027, to Tetzner. In Tetzner, a lifting force is imparted to a pivotable platform at a location centered between the sides of the platform. While Tetzner exerts a balanced lifting force, he requires an obtrusive frame in front of the platform to be able to develop the substantial lifting force that must be applied to the platform to effect elevation thereof.
U.S. Pat. No. 4,027,492, to Carpenter, discloses a pulley arrangement to distribute and reduce the requisite platform lifting force. However, the Carpenter structure has two noticeable drawbacks. First, the pulleys shown are of conventional construction and submerged in water with the platform lowered. The pulley are prone to being tangled with seaweed and other objects suspended in the water and are also likely to rust. Further, the cable is shown to be crossed from side to side on the apparatus. There is thus the potential of entangling the craft to be lifted and the cable.
U.S. Pat. No. 4,469,346, to Low, discloses a structure wherein the same problems associated with an exposed lifting cable are apparent.